The invention relates to development of a multiaxial high cycle fatigue test system.
Modern gas turbine engines need to maintain a balance between high performance, affordability, and design robustness. The rotating components of the turbine engine such as fan blades and turbine blades are subjected to high revolutions per minute during operation. As a result, one of the most common modes of failure in engine components is fatigue. This means that to improve the robustness of components, their fatigue behavior would have to be improved.
Component fatigue behavior can be improved, by improving either the material property or the component geometry or both. Material characteristics are typically studied by testing coupons. The effect of component geometry is lost in coupon tests. Finite element analysis can be used to simulate the actual component behavior to a certain extent. The best method would be to test the actual component by subjecting it to conditions similar to the operating conditions.
In a gas turbine engine, the fan blades and turbine blades rotate at high revolutions per minute during operation. The blades are subjected to a radial centrifugal force due to this rotation. Gas turbines have alternating stator and rotor blades. The stator blades guide the gas onto the rotor blades. As a rotor blade advances from one stator blade to the next, the gas pressure on the blade decreases and increases again. This results in the application of a cyclic load to the rotor blade. The blade also vibrates at its modal frequency under suitable conditions. These periodic loads result in a vibratory loading on the blade.
These patents relate to fatigue testing or axial and torsion testing. Sallberg et al have a multi-axial fatigue testing machine.
The invention relates to a multiaxial high cycle fatigue test system.
Vibratory loading causes high cycle fatigue failure in engine blades. To study and improve the fatigue life of gas turbine engine blades, or other test units such as components or material samples, a new test methodology has been proposed. According to this method, the blade or other test unit will be loaded multiaxially during testing, to simulate the actual operating conditions.
A multiaxial high cycle fatigue test system for testing bending, torsion, and tension of a test unit, comprises servo-hydraulic components, including a hydraulic service manifold, two small high frequency actuators along a first axis, and one large main actuator along a second axis. The large main actuator is used to apply a radial centrifugal force, and the two small actuators are used to apply vibratory loading; the two small side actuators being offset independently of each other, to enable the machine to apply both bending loads and torque to the test unit. The test unit is subjected to torsion loading when the traverse actuators move in phase, that is when both actuators move either in or out at the same time. The test unit is subjected to bending loading when the actuators move out-of-phase, that is one actuator moves in when the other moves out or vice-versa.
In the embodiment described in the detailed description, the test unit is a turbine blade. In general, the test unit may be any type of complete component, or a material sample, such as a portion of a component.